Various embodiments relate to noise reduction, and more particularly, to a method and apparatus for encoding an audio signal, for noise reduction.
Recently, communication services such as the Internet or satellite broadcasting are widely supplied, and also, audio-video (AV) devices such as digital versatile disks (DVDs) are also widely supplied. In accordance with the supply of these services and devices, demand for audio encoding involving efficiently compressing audio signals is increasing. Currently, adaptive conversion audio encoding apparatuses that take into consideration human hearing are mainly used. In such encoding processes, an audio signal which is in a time domain is converted into a frequency domain. In addition, a signal along a frequency axis is partitioned into frequency bands corresponding to frequency resolving power of hearing. Moreover, by considering human hearing, an optimal amount of data needed for encoding in each frequency band is calculated.
According to the data amount allocated to each of the frequency bands, the signal along the frequency axis is quantized. An example of an adaptive conversion audio encoding apparatus is a Moving Picture Experts Group (MPEG)-Advanced Audio Coding (2AAC) method that is standardized by the International Organization for Standardization (ISO)/International Electrotechnical Commission (IEC). Advanced audio coding (AAC, standard document: ISO/IEC 13818-7) is a standard lossy data compression method used in digital audio devices.
AAC provides more sample frequencies from 8 kHz to 96 kHz and up to 48 channels, and in AAC, bits may be variably allocated according to necessity even at a constant bit rate, and an audio signal may be changed into a modified discrete cosine transformation (MDCT) format, thereby enabling more efficient coding.